Technical Abstract:
In the US, rice has traditionally been classified on the basis of apparent amylose content. While apparent amylose content is clearly a key indicator of rice quality, the relationship between amylose content and cooking and processing quality is not absolute. Thus, secondary analyses of grain quality, such as starch paste viscosity tests, have been established to help distinguish rice with different cooking qualities. To identify the genes which control rice pasting characteristics, we examined the segregation of the genes for the primary enzymes involved in starch biosynthesis in a cross between the high amylose, strong pasting curve variety, Rexmont, and a low amylose, weak pasting curve variety, Toro-2. Somewhat surprisingly, we did not see a significant relationship between pasting characteristics and the genes for branching enzyme, debranching enzyme or soluble starch synthase. Granule Bound Starch Synthase (GBSS), however, was highly correlated with several parameters of the starch pasting curve, including starch paste breakdown and setback viscosity. In a agreement with GBSS playing a key role in determining pasting characteristics, we also found differences in the structural gene for GBSS between rice varieties with similar apparent amylose contents, but very different pasting properties.